1. Field of the Invention
The invention relates to a method and a device in a display unit of the LCD type for reducing time varying electric fields generated by the display unit.
2. Description of the Related Art
Display units have become more common in working localities and have recently been studied carefully with regard to different types of fields emitted therefrom. Different tests have shown that the emission has different effects on human tissue, but up to now the test results have been very contradictory.
One of the reasons for the results being contradictory and difficult to explain is probably that the picture of said field surrounding a display unit is very complex and comprises at least five different types of fields. Furthermore, in modern office premises there exists a high background level of emission from other electrical devices and installations.
A first type of field is the electrostatic field generating an electrostatic field between the surface of said display unit and any adjacent object having another potential, for instance a face.
Time varying electric fields or low frequency also surround a display unit. In frequently used cathode ray tubes said fields are comparatively weak, and therefore said fields have been considered harmless.
In a cathode ray tube which is included in the most common types of display units, a low frequency magnetic field is generated in the magnetic coils controlling the electron beam. It is very uncertain how the human being is affected by said field.
When the electron beam in a cathode ray tube hits the display surface an emission of radiation X-ray (s c soft emission) is generated. However, the major part thereof is stopped by the glass of the display unit.
Together with the visible light emitted from a display unit, a minor part of ultra-violet light is also emitted. Said ultra-violet light has more energy than the visible light.
Finally there is transmitted from the oscillator of the computer also radio frequency emissions, which all lower by at least a factor of 1000 than the present limit values.
In display units including cathode ray tubes it is previously known to cover the casing of the display unit with a conducting layer, and the front of the display unit with a transparent layer, the conducting ability thereof being such that higher electrical fields existing in these types of display units are attenuated almost completely around said unit. However, the weaker electrical fields, i.e., the fields having a strength of approximately 100 V/m, will remain to some extent.